Conventionally, for producing a compound semiconductor single crystal such as InP, a liquid-encapsulated Czochralski method (LEC method) or a vertical gradient freezing method (VGF method) has generally been used.
The LEC method is a method for encapsulating a raw material melt contained in a crucible by a liquid encapsulant such as B2O3, and growing a crystal while raising a seed crystal dipped in a raw material melt surface. Evaporation of a volatile element from the raw material melt or the grown crystal can be suppressed by the liquid encapsulant. When a semiconductor material contains a volatile element (e.g., V-group element), by growing a crystal while controlling vapor pressure of the volatile element, it is possible to prevent dissociation of the volatile element from the raw material melt or a surface of the grown crystal (vapor pressure control method). Accordingly, by using the LEC method, it is possible to produce a large-diameter and highly pure compound semiconductor single crystal. For example, a general LEC method is disclosed in Patent Document 1.
In Nonpatent Documents 1 and 2, techniques of producing large-diameter (3 inches, 4 inches) and low dislocation density InP single crystals by using the LEC method are disclosed. Importance of a shape of a solid-liquid interface of a raw material melt and a temperature gradient in a crystal growth direction is described.
The VGF method is for arranging a seed crystal in a crucible bottom, encapsulating a raw material melt contained in the crucible by an liquid encapsulant such as B2O3, and gradually cooling the raw material melt from the lower side while applying high pressure by an inactive gas to grow a crystal upward from the seed crystal. Because the temperature gradient in the crystal growth direction is small, it is possible to grow a low dislocation density compound semiconductor single crystal.
For example, a general VGF method is disclosed in Patent Document 2. According to the Patent Document 2, by growing a crystal with a growth speed in a crystal increased diameter part set to 20 mm/hr or more to effectively prevent generation of twin in the crystal increased diameter part, it is possible to obtain a compound semiconductor single crystal with high yield. Moreover, in Nonpatent Document 3, a technique of producing an InP single crystal by using a VGF method is disclosed.    Patent Document 1: WO03/060202    Patent Document 2: JP A 11-302094    Nonpatent Document 1: Jpn. J. Appl. Phys. Vol. 41 (2002) pp. 987 to 990    Nonpatent Document 2: Proc. of 14th intern. Conf. on Indium Phosphide and Related Materials p. 397 to 400    Nonpatent Document 3: Proc. of 14th Intern. Conf. on Indium Phosphide and Related Materials p. 413 to 415